This tutorial will help you to install Free SSL for the subdomain.  Please follow the step by step procedure to do this:

• Login to CloudStick dashboard.
• Select your server.
• Click on accounts.
• Select the Account that has a Subdomain you wish to install
• Click on SSL/TLS from the left-hand side menu.
• Select the Subdomain web application from the drop-down. Once you have selected, you can see the subdomain attached to the corresponding web application.
• Select the LetsEncrypt, then choose HTTP verification from the drop-down.
• We recommend unchecking HTTPS only and checking the option Both HTTP and HTTPS, if your domain has CloudFlare proxy enabled.
• If you don’t have Cloudflare, we recommend you to just choose, HTTPS only.
• Click on Deploy SSL, then you are done.